It takes a lot of energy and light bulbs to keep taxiway lights operating all night long. With an investment of $130,000, one Louisiana airport is reducing its need for both by storing the sun's energy for nighttime use.

Allen Taylor, airways systems manager for the Louisiana Department of Transportation and Development, has been working on improving airport lighting for years by recommending standards to the Federal Aviation Administration.

Several years ago, Taylor approached ADB Airfield Solutions about a concept he envisioned for low-profile fixtures similar to inset fixtures that would still meet all FAA specifications for medium-intensity runway lighting.

At the time, Taylor hadn't considered the idea of solar-powered LED fixtures. His goal was merely to end a problem that has plagued airports for years: one staff member would install taxiways lights and another would accidentally take them out with a lawn mower or other maintenance vehicle. A low-profile light fixture was his focus - until last year, when ADB briefed him about a new power supply it had developed that uses pulse width modulation (PWM) and consumes up to 90% less energy.

"My eyes opened wide because it was very interesting technology," Taylor recalls. "They wanted to test the advanced power supply as part of an airport lighting system which could easily be converted to PWM technology."

164 & Counting

Taylor selected the False River Regional Airport in New Roads, LA, to test the concept and fixtures. "False River is a well-maintained regional airport that I would say is one of the finest in the nation," he explains. "It has a full parallel taxiway system with conduit that was installed in 1997. We could phase in the implementation with minimal disruption to airport operations."

The airport took the taxiway lighting system out of service and began replacing six to 10 old quartz fixtures per day with the new equipment. With 164 fixtures to replace, the project took nearly six weeks.

Crews removed the 30-/45-watt isolation transformer from each fixture can, and then used the existing wiring and connectors for the new taxiway inset fixtures.

False River Regional replaced more than 160 quartz taxiway lights with new LEDs.

"We had some problems with the isolated transformer due to its age," Taylor explains. "It presented its own level of loss from an electrical standpoint. But, once we eliminated the transformer, we were left with two wires connected directly to the new LED fixture."

The new LED taxiway lights receive modulated DC current from an advanced power supply (APS) that provides the desired light intensity. The APS is powered by an AC inverter, which receives DC current from a solar-charged battery bank. Because the LEDs require so little energy, the lamps don't need 30-/45-watt isolation transformers at every fixture to regulate the amount of power coming into the unit, explains Miguel Vasquez-Lavado, product manager at ADB Airfield Solutions.

"We used the PWM concept to develop the advanced power supply which provides the right type and amount of current the LED wants," he adds. "By eliminating the requirement for electronics on the fixtures themselves, we were able to bring simplicity to the system and bypass other components."

The Payoff

The project was implemented at a cost of $130,000. However, the LED lighting allowed the airport to replace the existing 15-kilowatt regulator with an advanced power supply that draws less than 1 kilowatt of power. While standard current regulators weigh 400 to 1,000 pounds, the new power supply weighs 15 to 20 pounds and occupies a significantly smaller footprint. The original elevated standard taxiway fixtures each required installation of a 30- to 45-watt halogen lamp with a lifespan of 1,000 hours. The new LED lamps burn brighter with significantly reduced energy demands - and their rated lifespan is 100,000 to 200,000 hours.

A battery system stores solar energy to power taxiway lights at night.

"The 15-kilowatt regulator was necessary to handle the power load of illuminating 164 quartz lamp fixtures," says Taylor. "With the new LED lighting system in place, we were able to use modulated DC current that offered characteristics of AC power."

In other words, rather than using a system that consumed 15 kilowatts of power, False River Regional is able to essentially tap into battery power that's modified to resemble standard AC electricity. As a result, the airport's power consumption is dramatically reduced.

The airport's previous 45-watt bulbs required 7,425 watts of energy every day to power up. That utilized a 15,000-watt regulator to handle the expected capacity with the recommended reserve power, explains Vasquez-Lavado.

"It would take more than 40 solar panels and dozens of batteries to provide enough power to cover a 7,425-watt load," he relates. "In that type of situation, solar power would not be cost effective. With the new system, we reduced power consumption from 45 watts per fixture to just 4.5 watts. Power consumption dropped from 7,425 watts to 742 watts."

By using the new LED fixtures on an existing taxiway circuit, False River was able to use the same cabling, which reduced installation costs. The entire 10-panel solar array powers a 1,000-watt advanced power supply about the size of a standard DVD player. It collects about 1,700 watts of power from all the solar panels and stores the energy into a battery bank. From there, an inverter converts the DC power from the batteries into AC power used by the advanced power supply to generate the modulated DC for the LED lamps.

The new system draws 2 amps of power vs. 6.6 amps by the previous system. The lower current implies less power dissipation by the circuit cable and requires less expensive copper electrical cable.

"With less current on the circuit, the cable doesn't have to be as thick, which also reduces cost," notes Vasquez-Lavado. "The higher the current, the thicker the cable needs to be in order to withstand the power flowing through the system."

Switching from halogen to LED lights reduced maintenance costs. Then, ADB developed an advanced power supply to deliver the right type of power at the right time, and connected a solar panel to it to provide power to the entire system, Vasquez-Lavado summarizes. "We developed a completely green system that saves money and lasts longer," he relates.

Taylor describes the electric savings as significant. "By converting to a pulse width modulating (PWM) circuit design, we were able to dim the taxi lights and still meet the FAA requirements for light illumination out of standard LED lamps," he reports.

According to Taylor, there is a drawback with 6.6 LED taxiway fixtures that are currently available - the electronics that modulate the LED signal to mimic a halogen bulb contain more failure points than previous fixtures. Airport managers need to be mindful of the mean time to repair, he cautions.

"Originally, the MTBF (mean time between failure) on the taxiway LED system was higher than I felt was reasonable," he recalls. "I knew the technology is rapidly advancing, but I didn't want to put state dollars into changing over to an LED system until we were absolutely sure it was going to provide a higher cost-benefit ratio and a high MTBF."

Wider Application?

The pulse width modulated DC power system is working so well that Taylor envisions further advancements in LED technology that should allow airports to replace standard runway lighting systems with the power-saving LEDs.

As a pilot, he knows the significance of losing lights on approach to an airfield and is conservative about implementing the technology onto a runway system.

"We are interleaving the runway circuit in which every other runway fixture would be powered by a separate power supply (APS) circuit to further increase reliability of an LED light system," Taylor explains. "That way, if the airport were to lose one power supply, pilots would still be able to discern the definition of a runway outline from the remaining powered circuit."

Interleaving runway lighting would also allow the FAA to compare the costs of halogen and LED runway lighting. In addition, it could possibly allow airports to reduce the quantity of fixtures by increasing the space in between units, because LEDs are so much brighter.

"Right now, everyone in the aviation industry is pretty much doing the same thing when it comes to runway lighting," says Taylor. "Medium-intensity runway lights generally require a 45-watt quartz halogen lamp and L861-E threshold lights that use 120-watt quartz halogen lamps. The new system LED runway MIRL (medium-intensity runway lighting) test program for False River will have interleaved LED fixtures 2 feet from the edge of pavement while keeping the existing MIRL system in service 8 feet further outboard of the LED fixture."

The ability to create white light that matches the FAA criteria for color and intensity is currently delaying the development of LED lighting for runways, Taylor notes.

Solar LEDs

Because LED lights use so much less energy, airports can now install solar systems to power their lights. Carmanah Technologies in Victoria, B.C., partnered with ADB to develop the solar part of the system.

The advanced power supply uses PWM technology that generated an electrical cost savings of 85% to 90% compared to the traditional lighting system, Taylor reports.

"For me, to put in solar and realize only 10% to 15% of my traditional cost was not an easy decision," he explains. "However, I have difficulty spending money on solar systems to maximize energy consumption and decreasing MTBF by adding inverters, batteries and solar cells; all those can fail."

To play it safe, Taylor insisted on an automatic transfer switch that could transfer the taxiway lighting system to utility power in less than one second if the solar failed. Since the solar system was installed, he reports, it has never needed to tap into the backup utility power service.

"The solar array, charging control and 'cool cell' has done such a good job in maintaining proper voltage and battery temperatures in the 48-volt DC system that it has become the most efficient way of handling the battery maintenance replacement timeline," he says. "We use passive temperature regulating cool cell technology that uses water-filled walls and ceiling enclosure to collect heat during charging. That maintains a good battery temperature even during periods of extensive heat and, consequently, lengthens the life of the battery."

Testing New Fixtures

When the project was proposed by ADB, Taylor was excited to finally test a new low-profile L-861 fixture for the taxiways and runway. Traditionally, airports have been using L-852T omni-directional taxiway semi-flush lights.

Initially, Taylor mounted the lights 10 feet off the edge of the pavement. "I assumed we had a normal profile between the edge of the asphalt and the can elevation," he explains. "After many years, as additional overlays changed the slope profile cross-section, some of the cans were 10 to 12 inches below the surface of the asphalt. And, when grass was factored in, it made it even more difficult to maintain a visual perspective."

After consulting with airport engineer Gerald Babbin, Taylor moved them inboard so they were at the asphalt pavement elevation and grass wouldn't impede pilots' view of them.

Normally, the airport placed the fixtures 10 feet from the taxiway to prevent them from being damaged by jet blasts or pilots running off the taxiway.

Before the system could begin operating at False River, First Light Technologies of Victoria, B.C., was contracted to finalize the design and verify that it was installed to meet electrical codes. The company also made certain that the solar, battery and inverter power systems were appropriately sized to reduce the likelihood of system failure, notes Justin Taverna, company founder and managing director.

In addition to ensuring that documentation noted the exact location of installed components, the company provided technical support regarding the installation of the Sharp 175-watt solar panels.

"From our perspective, the project went very well," notes Taverna. "It was the first of its kind in the lower 48 states."

Bright Prospects

Taylor predicts that the series hard-wired solar lighting system using PWM from one or two power supplies will quickly become the new standard for runway and taxiway lighting as airports build new runways or taxiways, or convert existing airfields to go green. With the suggested modifications, he estimates airports can trim costs another 30% when employing PWM technology in new construction.

Vasquez-Lavado predicts that airports on small islands, where energy can cost 40 cents per kilowatt, will quickly embrace the new technology. ADB has installed similar systems in Windsor, Ontario; Orlando, FL; Atlanta, GA; Manchester, U.K.; and RAF Mildenhall, U.K. It will also install systems soon in the Caribbean and South America, where it reports high interest in solar.

He further predicts airports will eventually look to solar-driven LED lighting to power signs and obstruction lights. "Any LED products that use an advanced power supply with PWM can be powered by a solar panel which can completely eliminate any extra power expenses," notes Vasquez-Lavado.

Taylor hinted that ADB might announce a new lighting system at the Illuminating Engineering Society Airport Lighting Committee conference in October.

"ADB has developed a good, robust piece of industrial quality equipment," he says. "We haven't had a system failure since the solar-powered APS system was put in service in early April. I am very happy with it."